Heterosexual transmission of the human immunodeficiency virus is an increasingly important factor in the growth of the AIDS epidemic. Intravenous drug users account for the majority of heterosexual HIV transmission and AIDS in the United States and represent a critical link between high risk groups and the general population. Based on two ongoing studies of HIV seroprevalence in IV drug users and high-risk women, purpose to study the non- drug using heterosexual partners of known HIV seropositive individuals to assess the point-prevalence of infection and rates of seroconversion. 170 to 210 heterosexual partners (93 to 115 females and 75 to 92 males) of known HIV seropositives will be recruited from our cohorts. Subjects will be interviewed by a trained interviewer using a standard questionnaire to obtain demographic, medical and detailed behavioral data concerning sexual practices with the index seropositive case and other partners. Serum will be collected and tested for anti-HIV, HIV- antigen, and cytomegalovirus, hepatitis B virus, herpes simplex serologies as well as VDRL. Behavioral risk factors and laboratory predictors of HIV infection will be analyzed in partners and rates of infectivity of index cases will be determined. Predictors of infectivity in index cases, such as duration of HIV infection, presence of serum HIV-antigen, positive plasma HIV culture, and quantity of T-helper cells, will be assessed. By analyzing both infected index cases and their heterosexual partners we hope to more precisely define the transmission of HIV in heterosexual couples.